"All the external stuff is fixed at the same absolute position and hence generates a representation of absolute space," he said. "But when all the stuff is removed, the profound contribution of gait is revealed, which enables neurons to compute relative distances traveled."
The researchers also made a new discovery about the brain's theta rhythm. It is known that place cells use the rhythmic firing of neurons to keep track of "brain time," the brain's internal clock. Normally, Mehta said, the theta rhythm becomes faster as subjects run faster, and slower as running speed decreases. This speed-dependent change in brain rhythm was thought to be crucial for generating the 'brain time' for place cells. But the team found that in the virtual world, the theta rhythm was uninfluenced by running speed.
"That was a surprising and fascinating discovery, because the 'brain time' of place cells was as precise in the virtual world as in the real world, even though the speed-dependence of the theta rhythm was abolished," Mehta said. "This gives us a new insight about how the brain keeps track of space-time."
The researchers found that the firing of place cells was very precise, down to one-hundredth of a second, "so fast that we humans cannot perceive it but neurons can," Mehta said. "We have found that this very precise spiking of neurons with respect to 'brain-time' is crucial for learning and making new memories."
Mehta said the results, taken together, provide insight into how distinct sensory cues both cooperate and compete to influence the intricate network of neuronal activity. Understanding how these cells function is key to understanding how the brain makes and retains memories, which are vulnerable to such disorders as Alzheimer's and PTSD.
"Ultimately, understanding how these intricate neuronal networks function is a key to developing thera
|Contact: Mark Wheeler|
University of California - Los Angeles